Hey everyone. Well this is a complex issue here. During the Christmas holiday in 2010, I did a full tune up (well I did some and the mechanic in town did the #3 plug and wires since I couldn't do those) including a new cap and rotor. Well I had to replace the cap again last year due to white tips on the cap that were causing hard starts. Tonight I was at a scout meeting and the truck sat for 2.5 hours while the temperature dropped 20 degrees. I tried to start it 3 times and the starter cranked, the fuel pump primed and it wanted to run, but it died seconds after cranking it. I finally got it started and when I stopped for gas and food on the way back (60 miles), I could not reproduce the problem. It started right up even letting it sit for a while. I guessed it was the same problem and I was right. I took the 1/3/5 ignition wires off and unscrewed the cap to inspect the points and the tips were white. The rotor wasn't corroded and was still like new so I don't think that needs to be replaced. So I need ANOTHER new cap! I understand there was a TSB on corrosion, but I checked and there were no vents or screens in that distributor that I could see. The cap was as tight as I dared to make it, so no water got in. What am I dealing with here? I am supposed to take a trip this weekend and while I am going to pick up a cap tomorrow, could I put anything on the tips to prevent them from corroding again? I am attaching a photo of the cap.


EDIT: Which brand should I get? I can't get AC Delco in town and that was the one I used originally for the tuneup from RockAuto. Since this takes 15 minutes and it barely starts now, I want to replace it ASAP. My options are Carquest, Advance (BWD) or Napa ("Mileage Plus" or "Echlin" (which I have now)).

 

Never mind. Cap replaced with a Carquest premium cap with gold contacts and longer screws. No idea where those vents are unless they are not on this truck.

 

The good cap'n hook always says to coat the cap contacts -inside and out- with dielectric grease.
Maybe that's why.

Here's how I think that works.
When you draw an arc between two points there is always a miniscule 'spatter' of conductives and oxides. The oxides will not conduct but the non-oxidized metal will. And laid on top a bed of oxides forms a nice spark-bridge. The grease that isnt punched through will act to contain that spatter.

https://www.google.com/search?q=electrode+spatter

Secondly, that's why Aluminum cap electrodes are inferior. Caps didnt use aluminum even when houses were being wired with it. Aluminum is soft and easily eroded by arc.
Even when it's shielded by inert gases when welded, aluminum is trouble. Alum oxide is a vapor, per se. Spatter is conductive aluminum.

https://www.google.com/search?q=weld...uminum+spatter

 

Dielectric grease on cap contacts? Will that affect anything in addition to corrosion?

 

Read it again.. I was editing

 

Oh. Sorry. Thanks. I will get the dielectric grease and open it back up and also put some on the wire contacts.

 

I tried dielectric grease on the cap contacts and a couple years later they looked much worse than yours. The posts were mostly eaten away and the rotor was trashed. You can still try the grease if you want but I wouldn't expect it to help.

 

Hmmm.. now lets see. A couple years? did you read how old that cap was?

Were your contacts aluminum or plated?

In what way was your rotor trashed. .. What brand was it?

Thanks for the input.

 

I can't remember the specifics, I think it was aluminum contacts... Surprisingly everything was still running perfectly fine even though the contacts were pretty much gone. I think the dielectric grease is supposed to be for maintaining constant connections like spark plug connections and electrical plugs not distributors.

 

I'm an electrical engineer. I know the properties.

If you READ my reference links you might learn something. Just like I did. The ionized bridge between the rotor and cap contacts is just like an electric arc from a welder. Spatter when welding aluminum is a major problem. Both at the joint and the area around it. What's vaporized is usually an oxide, it is whitish. And what isnt vaprorized is called spatter and still a conductive metal. In the case of the alum cap posts, the grease would serve to contain both oxidation and spatter. Still inferior to brass, but should last longer than if not shielded, otherwise.

Dielecrtric grease isnt used to directly 'maintain contact' it is used to keep air {actually oxygen} out of the contact area and prevent the contacts from oxidizing/corroding. Dielectic grease doesn't conduct electricity.

Read my sig line, I damn well DONT expect you to just take my word for it. When you come across opinions contrary to what you think you know.. investigate!